A chargeable and dischargeable secondary battery has attracted attentions as a power source of an electric car, a hybrid electric car, etc., which has been proposed for overcoming air pollution of a conventional gasoline vehicle, diesel vehicle, and so on, which use fossil fuel.
Mid-to-large sized devices such as mid-to-large sized battery systems of vehicles formed by electrically connecting a plurality of battery cells according to the requirements for a high power output and a large capacitance. A pouch type lithium ion polymer secondary battery (a high voltage battery) that is mainly used as a unit battery in the mid-to-large sized battery systems has a relatively large size, excellent stability, and lightweight compared with a battery of the same series used in a small sized device, and thus is advantageous for slim and lightweight portable electronic devices.
However, when an internal pressure of a lithium secondary battery increases due to overcharging and swelling whereby a pouch type case swells occurs. When swelling occurs, a battery portion is modified, and thus, the battery is partially short-circuited.
In addition, when the battery is overcharged or exposed to a high temperature, gas with a high igniting possibility is generated due to a reaction between an electrolyte and an active material layer of a pole plate or a decomposition reaction of the electrolyte and the active material layer, thereby causing an ignition or an explosion of the battery.
Accordingly, Korean Patent Laid-Open Publication No. 10-1082498 A discloses a pouch type battery includes a pouch type case including a first resin layer, a second resin layer, and a metallic layer disposed between the first resin layer and the second resin layer. An electrode assembly is disposed in the pouch type case, wherein a venting portion is formed in the pouch type case. A total thickness of the venting portion corresponding to the metallic layer, the first resin layer, and the second resin layer is smaller than a thickness of the venting portion corresponding to the remaining portion.
However, the aforementioned pouch type battery has no path for discharging gas generated in the pouch type case. When the gas is introduced into a vehicle, the gas may adversely affect passengers or may react to a spark and so on to cause an explosion.
Accordingly, there is a need for a high voltage battery including a safety device that overcomes an internal pressure of a battery, which reaches a reference level, and rapidly prevents swelling to originally prevent damage or an explosion.
The description of the related art is to aid in understanding of the present disclosure and is not to be construed as conventional arts that are already known to those of ordinary skill in the art.